1. Field of the Invention
This invention relates to a solid-state scanning apparatus for reading a stationary original. And, more in particular, the present invention relates to a solid-state scanning apparatus which employs a solid-state image sensor comprised of CCD image sensing elements for converting light information into electrical signals by carrying out the raster type scanning.
2. Description of the Prior Art
For a communication system such as a facsimile and a digital copier, it is necessary to read an original to convert light information into electrical signals for transmission by wire or radio to a remote place where the original image is reproduced. In reading an original, it is common practice to use a line sensor which scans the horizontal sector of the original and to move either of the original or the line sensor with respect to the other in the direction vertical to the direction of the horizontal sector scan. This type of scanning is sometimes referred to as the "raster scanning."
When the line sensor is provided stationarily, an original must be moved with respect to the line sensor, which then requires to provide a movable original holder having a contact glass on which the original is placed. But, this approach is disadvantageous because it hinders a high speed operation partly due to a substantive mass of the original holder and partly due to involvement of a reciprocating motion of the original holder, the returning movement of which is nothing but waste of time. It is true that a special feeder may be provided for sheet-type originals in order to speed up the feeding operation. But, this does not solve the problems for thicker or book-type originals. Moreover, it is often observed that a sheet-type original is jammed in such a special feeder, thereby causing possible damages to the original.
Therefore, it is rather preferable to use a stationary contact glass on which an original is to be placed since various kinds of originals may be equally applicable without problems. If an original is kept stationary, then the line sensor must be moved to carry out the raster type scanning. The conventional scanning apparatus of this type, a typical example of which is disclosed in the Japanese Patent application Laid-Open No. 50-125614, was comprised of an illumination lamp, a lens, a mirror system and a CCD line sensor, all assembled as a unit. Such scanning apparatus was moved along the contact glass to carry out the raster type scanning, thereby reading the original held on the stationary contact glass.
It should, however, be noted that the above-described conventional solid-state scanning apparatus was relatively large and heavy, thereby imposing severe limitations on a high speed operation and presenting difficulties in moving the apparatus uniformly in speed as well as requiring a large driving force. Furthermore, when the above-described conventional apparatus is operated, the apparatus receives accelerating and decelerating forces as well as shocks at the end of the forward or backward stroke of movement. This can be a cause of shifting the setting position of various components of the apparatus, importantly the lens and the CCD line sensor. As may be easily understood, such shifting of the lens and/or the CCD line sensor is highly critical because the positional accuracy of the light-receiving surface of the CCD line sensor is approximately proportional to the inverse of the image reduction rate.
As is well known, there is a maximum size limitation in making a silicon wafer from which CCD's are manufactured. Thus, when a horizontal sector of an original to be scanned by a CCD line sensor is relatively large (e.g., a very wide original) or it is desired to increase the resolving power by having high-density picture elements, the horizontal scanning sector should be split into two or more sections with the provision of CCD image sensing devices arranged in a single line extending in the direction of horizontal scanning. If such a plurality of CCD devices are provided, the relative positional relationship among the CCD devices is vitally important for proper scanning.
It will be easily understood that such a split scanning cannot be easily employed in the conventional stationary-original-type scanning apparatus because shocks or vibrations imparted will destroy the proper setting of the lenses and/or CCD devices. In other words, the conventional scanning apparatus with a stationary original cannot be used for large-sized originals or high-resolving power applications.